In general, a plasma etching apparatus for etching a substrate such as a semiconductor wafer and a glass substrate for a liquid crystal display apparatus by using a plasma has been employed in a manufacturing process of semiconductor devices, or the like.
The plasma etching apparatus is typically configured to include, e.g., a vacuum processing chamber; a lower electrode provided in the processing chamber, the lower electrode also serving as a mounting table on which a substrate is mounted; and an upper electrode provided to face the lower electrode. A high frequency power is supplied to the lower electrode to generate a plasma of a processing gas. Further, the plasma etching apparatus includes a focus ring provided on the lower electrode to surround a periphery of the substrate in order to improve an in-plane uniformity of processing on the substrate.
Moreover, an inductive heating unit is provided inside the focus ring and the focus ring is inductively heated by a magnetic field generated by an induction coil placed in the vacuum processing chamber (see, e.g., Patent document 1).
[Patent document 1] Japanese Patent Application Publication No. 2008-159931
In the plasma etching apparatus, when a plurality of substrates is successively subjected to the plasma etching, the temperature of the focus ring is gradually increased from a room temperature as the focus ring is exposed to the plasma. For that reason, without dealing with such change of temperature, a first substrate firstly subjected to the plasma etching has a processed state different from those of a second and following substrates subjected to the plasma etching. To prevent the occurrence of such a problem, a plasma is conventionally generated in the vacuum processing chamber while a dummy substrate is mounted on the lower electrode and the focus ring is heated by the plasma, before the start of the processing of substrates.
If a plasma is generated in the vacuum processing chamber while no dummy substrate is mounted, the surface of an electrostatic chuck may be damaged by the plasma, the electrostatic chuck being provided on the lower electrode to electrostatically attract the substrate. Accordingly, as described above, the plasma is generated in the vacuum processing chamber while the dummy substrate is mounted on the lower electrode.
However, if the plasma is generated in the vacuum processing chamber to heat the focus ring by the plasma as described above, the focus ring and other members included in the vacuum processing chamber may be worn out. Further, if the focus ring is heated in this way, it becomes necessary to manage a frequency of using the dummy substrate or the like and provide an accommodation part (slot) for accommodating the dummy substrate.
Moreover, when the inductive heating unit is provided inside the focus ring and the focus ring is inductively heated by the magnetic field generated by the induction coil placed in the vacuum processing chamber, it is needed to provide, in advance, the inductive heating unit in the focus ring and the induction coil in the vacuum processing chamber. Accordingly, the heating mechanism for heating the focus ring has a complex structure, thereby increasing a manufacturing cost.
In the meantime, a processing shape at a peripheral portion of a processing-target substrate, e.g., a semiconductor wafer, may become different from those of other portions in the plasma etching apparatus. For example, when a hole is formed on a semiconductor wafer by a plasma etching, a processing shape at a peripheral portion of the semiconductor wafer may become thinner, thereby causing a diameter of the hole to be decreased. In this case, it is possible to improve the processing shape at the peripheral portion of the semiconductor wafer by cooling a focus ring. However, if the focus ring is cooled, an etching rate of a photoresist may be increased at the peripheral portion of the semiconductor wafer and a corresponding selectivity may be lowered.